Yes, call and request it via the booking line.
I believe Venom also recommends faxing your request to the resort directly within 10 days of arrival. If you don't have a fax, at least get the req on the reservation. Bed rails shouldn't be much of an issue at all.
Also - I know some people dislike that they don't go all the way down the bed. If you hop over to your local dollar store, grab a pool noodle, and toss it under the fitted sheet it will act in the same fashion as a bumper for a little extra security